feat(ecc): prune plugin 43→12 items, promote 7 rules to .claude/rules/ (#245)

ECC community plugin pruning: removed 530+ non-essential files
(.cursor/, .opencode/, docs/ja-JP, docs/zh-CN, docs/zh-TW,
language-specific skills/agents/rules). Retained 4 agents,
3 commands, 5 skills. Promoted 13 rule files (8 common + 5
typescript) to .claude/rules/ for CC native loading. Extracted
reusable patterns to EXTRACTED-PATTERNS.md.

.opencode/commands/plan.md

@@ -1,49 +0,0 @@
----
-description: Create implementation plan with risk assessment
-agent: planner
-subtask: true
----
-
-# Plan Command
-
-Create a detailed implementation plan for: $ARGUMENTS
-
-## Your Task
-
-1. **Restate Requirements** - Clarify what needs to be built
-2. **Identify Risks** - Surface potential issues, blockers, and dependencies
-3. **Create Step Plan** - Break down implementation into phases
-4. **Wait for Confirmation** - MUST receive user approval before proceeding
-
-## Output Format
-
-### Requirements Restatement
-[Clear, concise restatement of what will be built]
-
-### Implementation Phases
-[Phase 1: Description]
-- Step 1.1
-- Step 1.2
-...
-
-[Phase 2: Description]
-- Step 2.1
-- Step 2.2
-...
-
-### Dependencies
-[List external dependencies, APIs, services needed]
-
-### Risks
-- HIGH: [Critical risks that could block implementation]
-- MEDIUM: [Moderate risks to address]
-- LOW: [Minor concerns]
-
-### Estimated Complexity
-[HIGH/MEDIUM/LOW with time estimates]
-
-**WAITING FOR CONFIRMATION**: Proceed with this plan? (yes/no/modify)
-
----
-
-**CRITICAL**: Do NOT write any code until the user explicitly confirms with "yes", "proceed", or similar affirmative response.